1. Field of the Invention
This invention relates to apparatus for sorting randomly disposed articles in an article stream, and in particular, to a sorting apparatus wherein foreign objects, as dirt clods, are distinguished from marginally acceptable comestible products on the basis of the amount of time that an electrical signal representative of a physical characteristic of an article falls within a predetermined range of values.
2. Description of the Prior Art
The economic utility of in-field separation of acceptable from unacceptable harvested comestibles, such as tomatoes, is readily apparent. Not only does such in-field sorting significantly reduce labor costs, but it also shortens the transport time from farm to cannery or market, thus reducing waste due to spoilage.
Various types of sorting apparatus are known in the art. Several prior patents directed to sorting apparatus are listed in the background portion of the co-pending application of John D. P. Jones, Miles A. Smither and Elias H. Codding, Ser. No. 704,651, filed July 12, 1976, now U.S. Pat. No. 4,134,498, assigned to the assignee of the present invention. One general classification of sorting apparatus, known as a bichromatic sorting apparatus, utilizes light energy reflected from articles to be sorted at two predetermined wavelengths. For a bichromatic tomato sorter, these wavelengths typically fall at 550 nanometers (green light) and 660 nanometers (red light). Electrical characteristic signals, each corresponding in magnitude to the intensity of light reflected from the article at each respective wavelength, are typically utilized to generate a ratio classification signal which is then compared to a predetermined reference signal value. The article sort, when based upon color criteria, is effected when the classification signal exceeds (for example) the reference signal value.
Bichromatic sorting apparatus may utilize the article conveyor as the reference background intensity standard against which the intensities of reflected light signals are compared. U.S. Pat. No. 3,980,181 issued to Michael C. Hoover and Elias H. Codding and assigned to the assignee of the present invention exemplifies such an approach. The conveyor background may, during harvesting, change in color due to the settling of dust or dirt thereon. Thus, the reference standard against which light reflected from articles being sorted is compared may drift and change over time. Gain range amplifiers or the like may, however, be utilized to obviate this difficulty. Sorting apparatus such as that disclosed and claimed in the co-pending application of James F. Lockett, Ser. No. 704,697, filed July 12, 1976, and assigned to the assignee of the present invention utilize a non-reflective background against which light at the predetermined wavelengths reflected from the articles to be sorted is detected. This non-reflective background, or "black hole", is not altered by the deposition of dust, dirt or sediment found during harvesting and is believed advantageous for this reason.
Regardless of the background utilized, advances in prior sorting apparatus included the use of multiplexed sorting arrangements whereby signal outputs from a plurality of light sensing viewers arranged across a random article stream are sampled on a time-shared basis and sequentially applied to a classification and comparison network. The results of the classification and comparison (either a product-accept or a product-reject signal) are stored in predetermined locations in a random access memory for a predetermined time delay sufficient to permit the classified article to fall from the proximity of the viewed area to the proximity of an ejector element. At the expiration of the delay the memory storage location is addressed and the result of the classification and comparison (if a reject signal) is applied through a demultiplexer arrangement to activate the appropriate product ejector to thereby separate the rejected article from the article stream. The referenced U.S. Pat. No. 4,134,498 discloses and claims a sorting apparatus of this type. As a variation on the basic multiplexed sorter exemplified by this patent, a multiplexed sorting apparatus having an in-use testing capability to verify the operability of circuit components by testing signal outputs at selected test points in the multiplexed sorter circuitry at preselected channel times is disclosed and claimed in the co-pending application of James E. Lockett, Ser. No. 704,652, filed July 12, 1976 , now U.S. Pat. No. 4,088,227 also assigned to the assignee of the present invention. A power supply arrangement for a multiplexed sorting apparatus using the switching of capacitor elements is disclosed and claimed in the co-pending application of James F. Lockett, Ser. No. 704,697, filed July 12, 1976 and assigned to the assignee of the present invention.
The basic principle underlying the operation of any of the above-mentioned sorting apparatus (whether bichromatic or not) is that certain "acceptable" articles reflect a greater intensity of light at a given wavelength than is reflected by other articles, whether they are "marginally acceptable" or "rejectable". For example, in the bichromatic sorting apparatus, an article is "acceptable" if it reflects a greater intensity of light at one of the selected wavelengths than at the other selected wavelength such that the ratio signal produced by an "acceptable" article is greater than the ratio signal produced by other articles. Accordingly, a comparison of the ratio of electrical signals representative of reflected light intesities may be used to classify the "acceptable" from the "unacceptable" articles.
This principle is aptly illustrated in the case of a bichromatic tomato sorting apparatus graphically depicted on FIG. A. It is believed instructive to examine FIG. A, in which the electrical signal magnitude (in millivolts) representative of the intensity of light reflected from an article being sorted at red wavelength (660 nanometers) is indicated along the abscissa and the electrical signal magnitude representative of light from an article being sorted at green wavelength (550 nanometers) is indicated along the ordinate. A totally acceptable ripe tomato (reference point A) has a greater "red" signal magnitude (approximately 530 millivolts) than a "green" signal magnitude (approximately 65 millivolts). Conversely, an unacceptable unripe tomato (reference point B) has a "red" signal magnitude of approximately 125 millivolts and a "green" signal magnitude approximately equal to 300 millivolts. In the case of a bichromatic tomato sorting apparatus then, the ripe tomato yields a relatively high ratio of "acceptable" to "unacceptable" signals. (The ratio of the reflected signals is not illustrated in FIG. A). The converse, of course, is true for the unripe tomato, thereby establishing a fairly straightforward basis for a comestible article sort.
Tomatoes that are less than fully ripe (a "marginally acceptable" tomato as at reference point C) and a less than fully unripe tomato (as at reference point D) are readily observed to be closer to a "gray line" extending approximately 45 degrees from the origin of FIG. A. Tomatoes that are less than fully ripe, as illustrated at point C, are known in the art as "pink" or "breaker" tomatoes. These breaker tomatoes are marginally acceptable in that they may, with further ripening, provide an edible product. Unripe tomatoes, as at point D, are unacceptable.
However, these thus-far defined reference points on FIG. A are only part of the overall picture. No in-field sorting apparatus will recover from the field only comestible articles, that is, only ripe, "breaker" or unripe tomatoes. Practicality requires that these sorting apparatus also correctly take into account and reject foreign objects such as dirt clods, pieces of wood, rocks or the like which are invariably "harvested" together with the comestible products. Therefore, the underlying theory based on the reflectivity characteristics of articles to be sorted must be broad enough to accommodate the reflectivity patterns for these foreign objects which are randomly carried in the article stream being sorted. It has been observed, as illustrated on FIG. A at reference points E and F, that dirt clods, rocks and other foreign objects typically exhibit reflected light intensities which congregate just to the red side of the gray line. The outer limit intensity for foreign objects is illustrated at approximately point F. Experience has indicated that foreign objects typically reflect light intensities which define reference points which lie within a "dirt band" region between divergent straight lines p and q. An "acceptable product" band may then be seen to exist between the line p and the abscissa, while an "unacceptable product" band may be seen to exist between the line q and the ordinate. Some threshold intensities (illustrated as the lines t.sub.R and t.sub.G) eliminate extraneous noise signals from triggering a sort and are superimposed on FIG. A for this reason.
The facts graphically illustrated in FIG. A are generated by measuring the reflectivity characteristics of a stationary article. As such, FIG. A may be viewed as defining the "static" case. Not unexpectedly, in actual in-field use, some deviations from the "static" case illustrated in FIG. A have been observed. These deviations may be attributed to "dynamic" conditions inherent in an in-field environment. Thus, as shown in FIG. B, to comport with the realities and practicalities of in-field sorting, a time element must be superimposed onto the "static" findings depicted in FIG. A. Therefore, in FIG. B, the actual situation observed as a particular article progressively comes within the area viewed by a given viewer element is shown. As seen, the signal intensities representative of light at each of the bichromatic wavelengths reflected from the article varies as a function of time. Such variances are depicted in FIG. B as signal trace paths. In the case of the red and green tomatoes (reference points A' and B', respectively) FIG. B illustrates the trace paths corresponding to each article. It is noted that these trace paths shown on FIG. B ultimately lead to the signal values corresponding to the static reference points A and B which are shown in FIG. A. It is observed that the trace paths of ripe and unripe tomatoes fall entirely within the "acceptable product" band and the "unacceptable product" bands, respectively.
However, the trace path associated with the breaker tomato leading to and trailing from reference point C' (corresponding to reference point C on FIG. A) passes through the "dirt band". Thus, to prior art sorting apparatus, a marginably acceptable comestible product, as a breaker tomato, is classified as a foreign object and rejected since sorting apparatus of the prior art generates a product reject signal if a classification signal falls within the "dirt band". This, of course, is economically disadvantageous since breaker tomatoes are marginally acceptable and, with further ripening, become completely acceptable.
Accordingly, it would be of advantage to avoid economic waste due to the rejection of breaker tomatoes. Furthermore, it would be of advantage to provide an in-field sorting apparatus able to accurately differentiate between foreign objects, such as dirt clods and rocks and the like, and breaker tomatoes on the basis of the time duration of the trace paths within the "dirt band".